1. Technical Field
The present invention relates to swivel joints between adjacent pipe sections so that coaxial rotation can occur between the sections. More particularly, the present invention relates to a swivel joint which provides improved radial and thrust load transfer in the swivel joint.
2. General Background
In petroleum drilling, producing and servicing operations it is often advantageous to provide a flexible connection for adjacent pipe sections. This flexibility is normally provided through one or more swivel joints and swivel elbows arranged in such a manner as to allow relative rotation of two sections of piping in one or more planes. This relative movement at a joint is especially useful during the initial installation of a piping system, especially when the piping is temporary and will be removed and reinstalled numerous times during the life of the units.
Swivel joints have been used in many oil and gas well "service" applications where high pressure piping is connected between a truck (manifold units, pump trucks, blender trucks, etc.) and the wellhead for pumping "service" fluids at high pressures into a well formation or for testing the flow of petroleum fluids from the well formation. Such service fluids include acids, propants, gases, water mixtures and the like, which are used to stimulate the well formation or to "fracture" the formation to allow the petroleum to flow more freely. Such fluids also include special cements which seal off casing strings in the well bore or certain zones within the formation.
Swivel joints are also used in the piping systems of drilling rigs for oil and gas wells. These joints provide flexibility in piping used to handle drilling mud under pressure, certain types of flexible hydraulic lines used to control blowout preventor equipment, choke and kill lines associated with blowout preventor equipment, and temporary test lines which handle pressurized petroleum fluids from the well bore. Swivel joints are also used in piping connected to the wellhead for transmitting high pressure production oil and/or gas from the well.
Many conventional swivel joints use ball bearings to transmit the load between the connected pipe sections. Problems have been found in these types of swivel joints since they utilize ball bearings that move along raceways cut into the swivel body pieces. In these configurations, the surfaces of the raceways must be hardened in order to prevent the ball bearings from overloading when the swivel is under pressure. This hardening of the raceway surfaces is expensive and tends to reduce the impact, fatigue and/or low temperature resistance of the swivel member.
Another problem found in swivel joints which utilize ball bearings is in the assembly and disassembly of the units, especially during replacement of bearings and seals. It is often necessary, for example, to rotate or even disconnect the piping connected to the swivel joint in order to disassemble the swivel section. These assembly and disassembly operations are time-consuming and can give rise to assembly errors.
Many conventional ball bearing swivels are unduly heavy and unmanageable which causes problems since they have to frequently lifted and positioned manually. Ball bearing raceways are also susceptible to heavy wear such as "galling," "spalling" or indentation. Such wear can ultimately result in leakage of the compressive type seal normally used with conventional ball bearing swivels, resulting in the need to replace the expensive body piece.
Due to space requirement, ball bearing type swivel joints also tend to limit the radius of a flow passage possible for a given overall envelope size. By placing restrictions on the radius of the swivel joint elbow, swivel joints cannot use a larger flow radius in the elbow in order to reduce the eroding effects of abrasive fluids.
Swivel joints that use solid annular bearings instead of ball bearings have been suggested and several configurations are taught in U.S. Pat. Nos. 2,705,651; 3,384,428; 4,079,969 and 4,205,866. These joints, however, have limited strength because the loads are distributed from one pipe to another only through the bearing. Many of these joints also have separate radial and thrust bearings which add to the complexity and cost of the joint. Many also have bearings exposed to abrasive fluids flowing through the joint which reduces bearing life.